The research proposed in this P01 is driven by the concepts and methods of demography. All six projects focus on research on exceptional longevity. Longevity has proven to be remarkably plastic: environmental and genetic alterations can produce large increases in longevity. Our overarching goal is explore the nature of and limits to this plasticity. We address, among others, the following questions: . Are death rates declining at the highest ages and, if so, is the pace of decline accelerating or decelerating? . How much will best-practice life expectancy (in the record-holding population) increase over the course of the 21st century? . How long is life expectancy for the group of individuals who have the optimal characteristics (under the health conditions and levels of knowledge that currently prevail)? . What are the characteristics that enable a person to survive from his or her early 90s to age 100? . How much can dietary manipulation extend the life expectancy of Mexflies? . How much can the maximum observed lifespans of nematode worms be increased by combinations of genes and by environmental manipulations? . Does mortality tend to decline as a plant grows (with age), leading to "negative senescence" and extraordinary longevity for plants that manage to become large?